1. Field
The present invention generally relates to a cable expansion joint, and more particularly, to an optical cable expansion joint provided for use on loose tube jacketed fiber optic cable assemblies when an optical fiber(s) is bound or fixed at both ends.
2. Description of the Related Art
Loose tube fiber optic cables refer to an optical cable with loose tube structure. The fiber optic cable may consist of many layers. Except for the optical fiber, all other layers are used to protect the optical fiber and make the fiber optic transmission smooth and safe. The tube is inside the cable jacket and outside the optical fiber; the fibers are put inside the tube. The optical cable is referred to as “loose tube” because the outer diameter of the optical fiber is much less than the inner diameter of the tube. Thus, the optical fiber is shielded from being affected by the surrounding cable elements.
FIG. 1 illustrates a loose tube fiber optic cable system in which a twelve fiber (12F) microcore loose tube optical cable 101 is interposed between a USConec FOC Grade Multifiber Termination Push-on (MTP) connector 103 and a transition unit 105. The transition unit 105 is used to transition each of the twelve microfibers provided in the 12F microcore loose tube optical cable 101 into individual fiber outputs 107 (only two are shown) that are connected to one of twelve Standard Connector/Angled Physical Contact (SC/APC) connectors 109 (only two are shown).
There are two well-known problems associated with loose tube fiber optic cables. When subjected to elevated temperatures, the cable jackets of these loose tube fiber optic cables shrink. Additionally, the cable jackets of these loose tube fiber optic cables shrink and expand at a greater rate than aramid strength members and optic fibers protected by these cable jackets. When an optical fiber is constrained (i.e., bound at both ends by a connector or potted transition), the constrained optical fiber undergoes microbending that increases the insertion loss of the assembly.
As a counter-measure to this cable jacket shrinkage problem, manufacturers of fiber optic assemblies resort to two methods. First, manufacturers may anneal or pre-shrink the cable jacket to stabilize the cable jacket. However, this measure is impractical for use on long cable lengths. Second, manufacturers may leave a gap between the cable jacket end and a transition unit. This method is acceptable in many applications, but poses an area of mechanical weakness that reduces the reliability of the optical assembly when it is subjected to routine handling.